Flat panel display, light emitting module for use in flat panel display, and integrated circuit for use in light emitting module

ABSTRACT

The present invention discloses a flat panel display (FPD), a light emitting module for use in the FPD, and an integrated circuit for use in the light emitting module. The light emitting module includes: at least one light emitting device string; and a local circuit for controlling current through the light emitting device string and generating a local feedback signal, wherein the local circuit has a first terminal for receiving power, a second terminal for coupling to the light emitting device string to control the current through the light emitting device string, a third terminal for generating the local feedback signal, and a fourth terminal for coupling to ground. The wiring of the FPD is therefore simplified.

CROSS REFERENCE

The present invention claims priority to U.S. provisional applicationNo. 61/331,936, filed on May 6, 2010.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to a flat panel display (FPD), a lightemitting module for use in the FPD, and an integrated circuit for use inthe light emitting module; particularly, it relates to a FPD, a lightemitting module for use in the FPD, and an integrated circuit for use inthe light emitting module with simplified wiring.

2. Description of Related Art

FIG. 1 shows a conventional FPD, which includes a display module 10 fordisplaying an image; a power management circuit 20, which converts aninput voltage Vin to an output voltage Vout according to a feedbacksignal; and multiple light emitting device strings 32 for illuminatingthe display module 10. Each light emitting device string 32 includesmultiple light emitting devices connected in series. One end of eachlight emitting device string 32 is coupled to the output voltage Voutfor receiving power; the other end thereof is coupled to the powermanagement circuit 20 for adjusting current through the light emittingdevice string 32, and generating the feedback signal accordingly. Insome applications, the brightness of the light emitting device strings32 is adjustable; in such case, the power management circuit 20 receivesa dimming signal Dim, and adjusts the brightness of the light emittingdevice strings 32 according to the dimming signal Dim.

The power management circuit 20 may be as shown in FIG. 2. As shown inthe figure, the power management circuit includes a voltage convertercircuit 21, an error amplifier circuit 23, a minimum voltage selectioncircuit 25, and multiple current sources 27. The voltage convertercircuit 21 receives a feedback control signal Vc from the erroramplifier circuit 23, and the voltage converter circuit 21 converts theinput voltage Vin to the output voltage Vout according to the feedbackcontrol signal Vc. The error amplifier circuit 23 receives a minimumvoltage Vmin, and compares the minimum voltage Vmin with a referencevoltage Vref1 to output the feedback signal Vc. The minimum voltageselection circuit 25 receives N current sense signals CS1, CS2, CS3, . .. , CSN, and generates the minimum voltage Vmin according to the Ncurrent sense signals CS1, CS2, CS3, . . . , CSN. The multiple currentsources 27 are coupled to a first to an Nth different light emittingdevice strings 32, i.e., L1, L2, L3, . . . , LN, respectively, tocontrol current through respective light emitting device strings 32 (L1,L2, L3, . . . , LN).

The power management circuit 20 may also be as shown in FIG. 3, whereinthe transistors and resistors of the current sources 27 are providedoutside the integrated circuit chip 23, but the function and operationthereof are the same as the circuit shown in FIG. 2. In thisarrangement, the chip 23 needs three pins for each current source 27,that is, voltage signal pins LED1, LED2, . . . , LEDn, control signalpins Gate1, Gate2, . . . , Gaten, and current sense pins Sense1, Sense2,. . . , Sensen.

In the aforementioned conventional FPDs, regardless whether the currentsources 27 are provided inside or partially outside the chip, each lightemitting device string 32 needs to be coupled to the power managementcircuit 20 individually. The larger the size of the FPD is, the more thelight emitting device strings 32 are needed in number, and so are thenumber and length of wires required for connection. This means morecomplicate wiring and more space in need. For example, as shown in FIG.1, N light emitting device strings 32 require N+1 wires. Besides, if thelight emitting devices are connected in series in one light emittingdevice string 32 by a larger number, a higher operation voltage isrequired, which leads to higher manufacturing cost and safety concern.Furthermore, when the number of the light emitting device string 32 orthe number of the light emitting devices in one light emitting devicestring 32 changes, the power management circuit 20 and the wiring needto be modified correspondingly. These changes and modifications lead toa higher manufacturing cost.

In view of the foregoing, the present invention provides a FPD, a lightemitting module for use in the FPD, and an integrated circuit for use inthe light emitting module with a simplified wiring, as solutions to theaforementioned problems.

SUMMARY OF THE INVENTION

The first objective of the present invention is to provide a FPD.

The second objective of the present invention is to provide a lightemitting module for use in the FPD.

The third objective of the present invention is to provide an integratedcircuit for use in a light emitting module.

To achieve the objectives mentioned above, from one perspective, thepresent invention provides an FPD, comprising: a display module fordisplaying an image; a power management circuit, which converts an inputvoltage to an output voltage according to a feedback signal; a pluralityof light emitting modules for illuminating the display module, eachlight emitting module including: at least one light emitting devicestring, each light emitting device string having one or more lightemitting devices connected in series, and each light emitting devicestring having a first end and a second end, wherein the first end iscoupled to the output voltage for receiving power; and a local circuitfor controlling current through the light emitting device string andgenerating a local feedback signal, wherein the local circuit has afirst terminal for receiving power, a second terminal for coupling tothe second end of the light emitting device string to control thecurrent through the light emitting device string, a third terminal forgenerating the local feedback signal, and a fourth terminal for couplingto ground; wherein the local feedback signal of each light emittingmodule is coupled to a first node for providing the feedback signal atthe first node; and a common wiring cluster including: an output voltagecommon wire for delivering the output voltage; a feedback signal commonwire for delivering the feedback signal; and a ground common wire;wherein each light emitting module is electrically coupled to each ofthe common wires.

The aforementioned local circuit preferably receives a dimming signalfor adjusting current through the light emitting device string. In onepreferred embodiment, the local circuit may output a phase-shifteddimming signal generated by phase-shifting the dimming signal.

In one preferred embodiment, the local circuit may output a local faultsignal to indicate a fault condition, wherein the local fault signal ofeach light emitting module is coupled to a second node.

In another preferred embodiment, the local circuit further receivesserial data for adjusting an internal parameter of the local circuit.

From another perspective, the present invention provides a lightemitting module for use in an FPD. The light emitting module includes:at least one light emitting device string, each light emitting devicestring having one or more light emitting devices connected in series,and each light emitting device string having a first end and a secondend, wherein the first end is coupled to the output voltage forreceiving power; and a local circuit for controlling current through thelight emitting device string and generating a local feedback signal,wherein the local circuit has a first terminal for receiving power, asecond terminal for coupling to the second end of the light emittingdevice string to control the current through the light emitting devicestring, a third terminal for generating the local feedback signal, and afourth terminal for coupling to ground.

From another perspective, the present invention provides an integratedcircuit for use in a light emitting module for connecting to at leastone light emitting device string. The integrated circuit includes: acurrent source for controlling current through the light emitting devicestring via a node; and a sink-only voltage follower, which generates alocal feedback signal according to a voltage at the node.

In one preferred embodiment, the aforementioned integrated circuit mayfurther include an open detection circuit, which compares the voltage atthe node with a first reference voltage (or as an equivalentalternative, a first trip-point voltage) to determine whether the lightemitting device string is open-circuited.

In another preferred embodiment, the aforementioned integrated circuitmay further include a short detection circuit, which compares the nodevoltage with a second reference voltage (or as an equivalentalternative, a second trip-point voltage) to determine whether the lightemitting device string is short-circuited.

In another preferred embodiment, the aforementioned integrated circuitmay further include a phase-shift dimming circuit, which receives adimming signal and generates a phase-shifted dimming signal byphase-shifting the dimming signal.

In another preferred embodiment, the aforementioned integrated circuitmay further include a serial data bus decoder or a one-wire data busdecoder for receiving and decoding serial data, the serial data beingfor adjusting at least an internal parameter of the integrated circuit.

The objectives, technical details, features, and effects of the presentinvention will be better understood with regard to the detaileddescription of the embodiments below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram of a conventional FPD.

FIG. 2 shows a schematic diagram of the power management circuit 20 of aconventional FPD.

FIG. 3 shows a schematic diagram of the power management circuit 20 ofanother conventional FPD.

FIG. 4 shows a first embodiment of the present invention.

FIG. 5 shows a schematic diagram of a power management circuit 40 andmultiple light emitting modules 52 of the first embodiment.

FIGS. 6A and 6B show a more specific embodiment of a local circuit 56.

FIG. 6C shows a more specific embodiment of a sink-only voltage follower561.

FIGS. 6D and 6E show a more specific embodiment of a current source CSL.

FIG. 7 shows another embodiment of the present invention.

FIG. 8 shows a schematic diagram of a power management circuit 40 andmultiple light emitting modules 52 of the embodiment shown in FIG. 7.

FIG. 9 for example shows signal waveforms of dimming signals Dim, Dimo1,Dimo2, and Dimo3 shown in FIG. 8.

FIG. 10 shows a more specific embodiment of the local circuit 56 shownin FIG. 7.

FIG. 11 shows a phase-shift dimming circuit 567, which for example mayinclude a delay locked loop (DLL) 5671.

FIG. 12 shows the phase-shift dimming circuit 567, which for example mayinclude a pulse width (PW) mirror 5673.

FIG. 13A shows a more specific embodiment of the PW mirror 5673 shown inFIG. 12.

FIG. 13B shows waveforms of signals at different nodes shown in FIG.13A.

FIG. 14 shows an example of the waveforms of dimming signals Dim andDimo.

FIG. 15 shows an embodiment of the phase-shift circuit 567.

FIG. 16 shows another embodiment of the phase-shift circuit 567.

FIG. 17 shows another embodiment of the present invention.

FIGS. 18A and 18B show a more specific embodiment of the local circuit56.

FIG. 18C shows a more specific embodiment of a valley detection circuit562.

FIG. 19 shows another embodiment of the present invention.

FIG. 20 shows another embodiment of the present invention.

FIG. 21 shows another embodiment of the present invention.

FIGS. 22A and 22B show that the local circuit 56 may include a serialdata bus decoder 568 or a one-wire data bus decoder 569 internally.

FIGS. 23A-23H show synchronous and asynchronous buck, boost, invertingand buck-boost converters.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 4 shows a first embodiment of the present invention. As shown inthe figure, an FPD includes a display module 10 for displaying an image;a power management circuit 40, which converts an input voltage Vin to anoutput voltage Vout according to a feedback signal FB; and multiplelight emitting modules 52 for illuminating the display module 10. Eachlight emitting module 52 includes: at least one light emitting devicestring 54, each light emitting device string 54 having one or preferablymore light emitting devices connected in series, and each light emittingdevice string 54 having a first end E1 and a second end E2, wherein thefirst end E1 is coupled to the output voltage Vout for receiving power;and a local circuit 56 having pins Vcc, CS, LFB, and GND. Pin Vccreceives power and provides an internal supply voltage to the localcircuit 56 (the internal supply voltage is referred to as Vcchereinafter). The internal supply voltage Vcc for example is generatedby the output voltage Vout, or by other proper sources, such as theinput voltage Vin or other DC voltages. Pin CS of the local circuit 56is coupled to the second end E2, for controlling current through thelight emitting device string 54. Each local circuit 56 generates a localfeedback signal LFB at pin LFB, and the local feedback signal LFB iscoupled to a feedback signal pin FB of the power management circuit 40to provide the feedback signal FB. The feedback signal FB is determinedby the lowest one of all the local feedback signals LFB (details will bedescribed later). In this embodiment, if it is desired for the displaymodule 10 to be capable of providing a dimming function, the localcircuit 56 may further include a pin Dim. Each local circuit 56 receivesthe same dimming signal Dim, and adjusts current through each lightemitting device string 54 according to the dimming signal Dim. The localcircuit 56 does not need the pin Dim if the display module 10 does notneed to provide the dimming function.

It can be found by comparing FIG. 4 with FIG. 1 that, in the presentinvention, because of the local circuit 56 which is provided locally andconnected with the light emitting device string 54 to become one localmodule, i.e., the light emitting module 52, the wiring is simplifiedbecause the light emitting modules 52 may all share the same wires inthe FPD. That is, the light emitting modules 52 may be commonlyconnected to the same wire for a specific function, instead of connectedto different wires for different modules or light emitting devicestrings respectively). The number of the wires is greatly reduced tofour, including: an output voltage common wire for delivering the outputvoltage Vout (if the internal supply voltage Vcc is generated by theoutput voltage Vout); a feedback signal common wire for delivering thefeedback signal FB (LFB); a ground common wire for connection to groundlevel GND; and a dimming signal common wire for delivering the dimmingsignal Dim. In fact, if the display module 10 does not need to providethe dimming function, the dimming signal common wire can be omitted, andthe number of the common wires is further reduced to three. In the priorart shown in FIG. 1, if there are N light emitting device strings 32,N+1 wires are needed. In contrast, the present invention obviously savesspace effectively. Besides, in the prior art shown in FIG. 1, fordifferent number of light emitting device strings 32, the internalcircuit and the number of pins of the power management circuit 20 needto be modified or re-designed. In the present invention, the same powermanagement circuit 40 can be used to cooperate with any number of lightemitting device strings 32 without changing the internal circuit or thenumber of pins, as long as the total power required does not exceed thelimit. Therefore obviously, the present invention is more advantageousthan the prior art.

FIG. 5 shows the relationship between the power management circuit 40and multiple light emitting modules 52. The feedback signals LFB of allthe local circuits 56 are coupled to the same node, which is coupled tothe feedback signal pin FB of the power management circuit 40. Forbetter understanding, a feedback circuit 42 including resistors R1 andR2 is shown in the figure. This explains how the feedback signal FBincludes information related to the output voltage Vout and informationrelated to the lowest of the feedback signals LFB. The feedback signalFB is fed back to the power management circuit 40 for controlling theoutput voltage Vout. Note that even though FIG. 4 does not show thefeedback circuit 42, FIGS. 4 and 5 are not conflicting with each otherbecause the feedback circuit 42 may be considered as a part of the powermanagement circuit 40, i.e., a circuit 40′ shown in FIG. 5 may beconsidered as corresponding to the power management circuit 40 shown inFIG. 4. Besides, the feedback circuit 42 does not have to include theresistors R1 and R2; one or both of the resistors R1 and R2 may beomitted in a circuit design wherein the feedback signal FB is aboutequal to the minimum of the local feedback signals LFB.

The output voltage Vout is provided to all the light emitting modules52. However, due to variation resulting from manufacture, the voltageacross the light emitting device string 54 may be different from oneanother. A higher voltage drop across one light emitting device string54 results in a relatively lower voltage at the pin CS of thecorresponding local circuit 56. If the voltage at the pin CS is too low,the local circuit 56 cannot control current through the correspondinglight emitting device string 54 as desired. Therefore, the outputvoltage Vout must be high enough to ensure all the voltages at pins CSof all the local circuits 56 are high enough. The voltage at pin CS ofeach local circuit 56 is related to the feedback signal LFB; in otherwords, to ensure that all the light emitting modules 52 operatenormally, a proper feedback signal FB needs to be generated according tothe lowest one of the feedback signals LFB, so that the output voltageVout can be controlled accordingly.

FIG. 6A shows a more specific embodiment of the local circuit 56. In apreferred embodiment, the local circuit 56 may be integrated as anintegrated circuit. As shown in FIG. 6A, a controllable current sourceCSL receives the dimming signal Dim, and adjusts the brightness of thelight emitting device string 54 by controlling current through the lightemitting device string 54 via pin CS (if the dimming function is notrequired, the controllable current source CSL may be a simple currentsource and it does not have to be controlled by the dimming signal Dim).If a voltage Vcs supplied to the controllable current source CSL is nothigh enough, the controllable current source CSL cannot operatenormally. Therefore, the voltage Vcs must be maintained at a voltage atleast higher than a minimum level which keeps the controllable currentsource CSL operating normally. One input terminal of a sink-only voltagefollower 561 receives the voltage Vcs at node CS, the other inputterminal, after biased by a DC bias Vos, is coupled to an outputterminal. In other words, the output of the sink-only voltage follower561 is maintained at the voltage Vcs+Vos. The DC bias Vos indicates anoffset bias between the two input terminals of the sink-only voltagefollower 561; it does not have to be a physical device. The purpose ofthis DC bias Vos is to provide flexibility to circuit design, so that itis easier to adjust the target of the feedback signal LFB, or to achieveother purposes in circuit design. This DC bias Vos does not have toexist, i.e., the DC bias Vos may be 0 or any other value. The voltageVcs+Vos is outputted as the feedback signal LFB.

The voltage follower 561 is a sink-only type device for the reasonbelow. Because the feedback signals LFB of all the local circuit 56 arecoupled to the same node, when the voltage follower 561 is sink-only,the voltage at that node is determined by the lowest one among thefeedback signals LFB; that is, the feedback signal FB is determined bythe lowest one of the feedback signals LFB.

FIG. 6B shows another embodiment of the local circuit 56. Thisembodiment further provides an open-circuit detection function and astart-up error prevention function. As shown in the figure, except thesame parts as FIG. 6A, the circuit further includes an open detectioncircuit. An embodiment of the open detection circuit for example is acomparator 563, which compares the voltage Vcs at node CS with areference voltage Vref2. In normal condition, the voltage Vcs is higherthan the reference voltage Vref2. If the light emitting device string 54is open, the voltage Vcs is close or equal to 0, lower than thereference voltage Vref2. Therefore, the output of the comparator 563indicates whether the light emitting device string 54 is open-circuited.However, when the circuit is starting up, the voltage Vcs is naturallylower than the reference voltage Vref2; in such a condition, the lightemitting device string 54 is not open-circuited, but it may bedetermined as open-circuited. Therefore, in this embodiment, a start-upindication signal Vst (an indication signal generated when the circuitis starting up) is inputted to an input terminal of an OR logic gate565, and the output of the comparator 563 is inputted to the other inputterminal of the OR logic gate 565. An output of the OR logic gate 565controls a switch Q1. When the light emitting device string 54 isopen-circuited, and the circuit is not in start-up phase, the switch Q1is OFF, i.e., the output of the voltage follower 561 in the localcircuit 56 is not sent out so it does not affect the voltage at thecommon node connected by all the feedback signals LFB. Therefore, thepower management circuit 40 will not incorrectly increase the outputvoltage Vout according to the output of the voltage follower 561 in thislocal circuit 56. On the other hand, when the circuit is in start-upphase, or when the light emitting device string 54 is notopen-circuited, the output of the OR gate 565 turns ON the switch Q1,such that the output of the voltage follower 561 in this local circuit56 is effectively provided to the common node of the feedback signalLFB. Note that under the teaching of the present invention, thoseskilled in this art can modify the above arrangement in various wayssuch as interchanging the positive and negative input terminals of thecomparator 563, or using a different type of transistor for the switchQ1; and the logic gate 565 does not have to be an OR gate. Thecomparator 563 and the reference voltage Vref2 can be replaced by alevel-detector circuit with a trip-point voltage equal to Vref2. Thelevel-detector circuit can be as simple as a Smith-trigger or a logicgate with proper input trip-point voltage. All such modifications shouldbelong to the scope of the present invention as long as they can achievethe functions of open-circuit detection and start-up error prevention.

One simplest form to embody the sink-only voltage follower 561 is shownin FIG. 6C, which is a PNP bipolar junction transistor (BJT). Thesink-only voltage follower 561 may be embodied in other more complicatedforms, which are readily conceivable by those skilled in this art underthe teaching of the present invention, and therefore is not redundantlyexplained here.

If the controllable current source CSL is a simple current source, itcan be a circuit as shown in FIG. 6D. When the circuit is stable, thecurrent through the transistor M is equal to REF/R, wherein thetransistor M may be replaced by a BJT. If it is required to provide adimming function, the controllable current source CSL may be as shown inFIG. 6E, wherein the dimming signal Dim is a pulse width modulation(PWM) signal. When the dimming signal Dim is at high level, the switchQ2 turns OFF, and the switch Q3 turns ON; the controllable currentsource CSL functions as a simple current source in FIG. 6D. When thedimming signal Dim is at low level, the switch Q2 turns ON, and theswitch Q3 turns OFF; the voltage at the negative input terminal of theamplifier is higher than the voltage at its positive input terminal, sothe transistor M turns OFF. Thus, the average current through thetransistor M is controlled by a duty ratio of the dimming signal Dim.That is, the average current through the light emitting device string 54may be controlled by the duty ratio of the dimming signal Dim. Such PWMdimming method is a major trend in FPDs and therefore the presentinvention focuses on explaining how it works, but certainly, the presentinvention is applicable to FPDs using other dimming methods.

FIG. 7 shows another embodiment of the present invention. Thisembodiment is different from the first embodiment in that, the dimmingsignal Dim is not coupled to all the local circuits 56 at a common node;instead, it is coupled to a dimming signal input pin Dimi of one of thelocal circuits 56. The local circuit 56 which receives the dimmingsignal Dim phase-shifts the dimming signal Dim and then outputs thephase-shifted dimming signal from a dimming signal output pin Dimo to adimming signal input pin Dimi of another local circuit 56, and so on.“Phase-shift” means that the dimming signal Dim is delayed for a periodof time while keeping the same pulse width. In this way, the lightemitting device strings 54 will not turn ON and OFF all at the sametime. On the one hand, this avoids drastic brightness fluctuation in theFPD (even though such fluctuation may not be perceivable by human eyes,it still may impact the quality of images to some extent); on the otherhand, because it is not required to provide the dimming signal Dim toall the local circuits 56, the dimming signal Dim is less likelydistorted, nor is it required to pull up the voltage level of thedimming signal Dim.

FIG. 8 shows a schematic diagram of the power management circuit 40 andmultiple light emitting modules 52. FIG. 8 shows the cascaded connectionfor the dimming signal as mentioned above, wherein the dimming signalDim (or Dimo1, Dimo2, . . . ) is received by the dimming signal inputterminal Dimi of one local circuit 56, phase-shifted by this localcircuit 56, and then outputted from the output terminal Dimo of thislocal circuit 56 to the input terminal Dimi of another local circuit 56.In FIG. 8, the power management circuit 40 is shown as an AC-DCconverter for example; certainly, the power management circuit 40 is notlimited to the AC-DC converter, but also can be a DC-DC converter suchas the ones shown in FIGS. 23A-23H.

FIG. 9 illustrates one possible arrangement of the phase-shift dimming.Referring to both FIGS. 8 and 9, a first local circuit 56 receives thedimming signal Dim at its dimming signal input terminal Dimi, andgenerates a dimming signal Dimo1, which is outputted from its dimmingsignal output terminal Dimo to the dimming signal input terminal Dimi ofa second local circuit 56. The second local circuit 56 generates adimming signal Dimo2 according to the dimming signal Dimo1, and sendsthe dimming signal Dimo2 to the dimming signal input terminal Dimi of athird local circuit 56, and so on. In the embodiment of FIG. 9, thefalling edge of a previous dimming signal triggers the rising edge of anext stage dimming signal Dim; the detailed embodiment of the circuitwill be described later. Note that phase-shifting can be done in variousways other than triggering the rising edge of a next stage dimmingsignal by the falling edge of a previous dimming signal.

A local circuit 56 capable of phase-shifting a dimming signal may be asshown in FIG. 10, wherein the local circuit 56 further includes aphase-shift dimming circuit 567. The phase-shift dimming circuit 567 forexample includes a delay locked loop (DLL) 5671 as shown in FIG. 11, ora pulse width (PW) mirror 5673 as shown in FIG. 12. In FIG. 10, it isthe phase-shifted dimming signal Dimo which controls the controllablecurrent source CSL; however, the controllable current source CSL cancertainly be controlled by the pre-phase-shifted dimming signal Dimiinstead.

FIG. 13A shows a more specific embodiment of the PW mirror 5673 shown inFIG. 12, and FIG. 13B shows signal waveforms at several nodes shown inFIG. 13A. Referring to FIGS. 13A and 13B, how the PW mirror 5673duplicates and delays the dimming signal Dim is described below. Asshown in the figures, signal A is the dimming signal Dim, and signal Gis the phase-shifted dimming signal Dimo1 (with a shifted phase to thedimming signal Dim). Signal B is obtained from the falling edge ofsignal A (signal B is at high level at a first falling edge of signal A,and changes to low level at a second falling edge of signal A, and soon; i.e., signal B is a standard frequency division signal triggered bythe falling edges of signal A). In FIG. 13A, the function of the uppercircuit is to generate signal E according to signal A, and the functionof the lower circuit is to generate signal F according to signal A. Asshown in FIG. 13B, signal E is obtained by delaying and duplicating odd(a first, a third, a fifth, . . . ) duty cycles of signal A, and signalF is obtained by delaying and duplicating even (a second, a fourth, asixth, . . . ) duty cycles of signal A (the rising edges of signals Eand F follow the falling edges of signal A). Thus, by combining signalsE and F via an OR gate G1, signal G can be obtained.

FIG. 14 shows signal waveforms representing another relationship betweenthe dimming signals Dim and Dimo, which indicates that the dimmingsignal Dimo may be generated by different embodiments. FIGS. 15 and 16show two embodiments which generate the waveforms shown in FIG. 14.Those skilled in this art can readily conceive other specificembodiments of the phase-shift dimming circuit 567 from the spirit ofthe embodiments shown in FIGS. 15 and 16. The scope of the presentinvention is not limited within these two embodiments.

In the embodiments shown in FIGS. 15 and 16, slopes of signal C and C′are determined by the voltage-controlled current source VCCS1, and theterm “voltage-controlled current source” means that the current throughthe current source can be controlled by a voltage. In FIG. 15, signal Ais delayed by a short delay circuit DC for a short period. The signalgenerated by the short delay circuit DC and an inverted signal of signalA are inputted to an AND gate G6; the AND gate G6 generates a shortpulse signal related to the falling edge of signal A, which is signal Bshown in FIG. 14. Signal B controls a transistor switch Q. When signal Bis at high level, the transistor switch Q turns ON, and node C is pulledto Vref, such that the output signal (signal D) of a comparator Comp4changes to high level. When signal B is at low level, the transistorswitch Q turns OFF, and the capacitor C5 discharges via the currentsource VCCS1; when the voltage at node C is decreased to Vref4, theoutput signal (signal D) of the comparator Comp4 changes to low level.The discharge rate of the capacitor C5 (i.e., the decrease rate ofsignal C) is determined by the current source VCCS1. Signal A and thefeedback signal D are compared by the comparator Comp3, and then thecomparison result is processed by the low-pass filter LPF to obtain anaverage, i.e., the voltage signal Vx, which is used to control thecurrent source VCCS1. As such, the current of the current source VCCS1is feedback adjusted to a proper value. When the pulse width of signal Dis relatively wide, the discharge rate of the capacitor C5 is controlledto increase, and when the pulse width of signal D is relatively narrow,the discharge rate of the capacitor C5 is controlled to decrease, suchthat the pulse width of signal D will finally balance at the same pulsewidth of signal A.

Similarly, FIG. 16 shows that when signal B is at high level, thetransistor switch Q turns ON, and node C′ is coupled to ground, suchthat the output of the comparator Comp 4 (signal D) changes to highlevel. When signal B is at low level, the transistor switch Q turns OFF,and the capacitor C5 is charged by the current source VCCS1; when signalC′ is higher than a reference voltage Vref5, signal D changes from highlevel to low level. In this circuit, signal D is also fed back to thecomparator Comp 3, and the output of the comparator Comp 3 passesthrough the low-pass filter LPF to generate the voltage signal Vx, forcontrolling VCCS1. Thus, the slope of signal C′ is properly determined.

FIG. 17 shows another embodiment of the present invention. Referring toFIG. 17 and also FIG. 18A, this embodiment is different from theembodiment shown in FIGS. 7 and 10 in that, in this embodiment, thelocal circuit 56 detects whether the light emitting device string 54 isshort-circuited besides detecting open-circuit. A short circuitcondition means that one or more light emitting devices in the lightemitting device string 54 are short-circuited. When a short-circuitcondition is detected, a local fault signal FT is generated to indicatean abnormal condition. In this embodiment, the local fault signals FT ofall the local circuit 56 are coupled to a same node, and outputted as afault signal Fault; that is, when any one of the local circuits 56generates the local fault signal FT, an abnormal condition is indicatedby the fault signal Fault.

A basic method to detect whether the light emitting device string 54 isshort-circuited is to check if the voltage Vcs at node CS shifts towardthe output voltage Vout abnormally (when the output voltage Vout ispositive, it is checked whether the voltage Vcs is too high; when theoutput voltage out is negative, it is checked whether the voltage Vcs istoo low). Referring to FIG. 18A, the local circuit 56 includes the shortdetection circuit. In this embodiment, as an example, the shortdetection circuit includes a valley detection circuit 562 and a Smithtrigger 564. For easier understanding, let us first assume that thevoltage Vcs is a static DC voltage (static operation); in thiscondition, the output voltage of the valley detection circuit 562 isequal to voltage Vcs (in fact, the valley detection circuit 562 is notrequired if the voltage Vcs is a static DC voltage). When the voltageVcs at node CS exceeds a transition point (also referred as thetrip-point) voltage of the Smith trigger 564, the Smith trigger 564generates the fault signal FT. The Smith trigger 564 may be replaced bya comparator, comparing the voltage Vcs at node CS with a predeterminedreference voltage. When the voltage Vcs at node CS is higher than thereference voltage, the comparator generates the fault signal FT. In adynamic operation condition where the voltage Vcs is fluctuating, not astatic DC voltage, the valley detection circuit 562 is required. Atypical case of the dynamic operation is PWM dimming. The voltage Vcs isfluctuating in PWM dimming as thus. When the dimming signal Dimo is atlow level, the controllable current source CSL does not operate, and thecurrent through the light emitting string 54 is zero or close to zero;the voltage drop across the light emitting device string 54 is low, sothe voltage Vcs at node CS is closer to the output voltage Vout. On theother hand, when the dimming signal Dimo is at high level, thecontrollable current source CSL operates normally; the voltage dropacross the light emitting device string 54 is relatively high, so thevoltage Vcs at node CS drops to a low level. In such condition where thecircuit provides the PWM dimming function, the function of the valleydetection circuit 562 is thus. If a short-circuit condition happens inthe light emitting device string 54 when the dimming signal Dimo is athigh level, the voltage drop of the light emitting device string 54 isrelatively lower than that in a normal condition, i.e., the voltage Vcsat node CS is relatively closer to the output voltage Vout. In otherwords, when the dimming signal Dimo switches between the low level andthe high level, for a light emitting device string 54 operatingnormally, the valley of the voltage Vcs at node CS is a normal lowvoltage; however, for a light emitting device string 54 wherein theshort-circuit condition occurs, the valley of the voltage Vcs at node CSabnormally shifts toward the output voltage Vout. Therefore, todetermine whether the voltage Vcs is close to the output voltage becauseof short-circuit, the valley detection circuit 562 is required fordetecting the valley of the voltage Vcs. As seen from the above, if thecircuit does not provide the PWM dimming function (static operation),the valley detection circuit 562 is not required; in this case, thevoltage Vcs may be directly inputted to the Smith trigger 564, or thevoltage Vcs may be compared with a predetermined reference voltagedirectly.

FIG. 18B shows another embodiment of the local circuit 56. In thisembodiment, the local fault signal FT is generated when either theshort-circuit condition or the open-circuit condition happens. In thefigure, the circuit 566 has a function similar to a logic OR gate. Whenthe voltage Vcs is lower than the reference voltage Vref2, and thestart-up indication signal Vst is at low level (indicating that theopen-circuit condition happens in the light emitting device string 54while the circuit is not in start-up phase), the output of the logic ORgate 565 is at low level, so the switch Q4 turns ON, and the local faultsignal FT is outputted from the circuit 566. On the other hand, if theoutput of the Smith trigger 564 is at high level, (indicating that theshort-circuit condition happens in the light emitting device string 54),the switch Q5 turns ON, and the circuit 566 also outputs the local faultsignal FT with high level.

The valley detection circuit 562 shown in FIGS. 18A and 18B can beembodied in various ways. FIG. 18C shows an embodiment of the valleydetection circuit 562. In this embodiment, there is a fixed voltagedifference between the output of the valley detection circuit 562 andthe lowest voltage (valley) of the voltage Vcs, but this is alrightbecause such difference can be compensated by setting a propertransition point of the Smith trigger 564; the primary function of thecircuitry is not impacted.

Furthermore, for the embodiments illustrated in FIGS. 17 and 18A-18C,because the FT output of all the light emitting modules 52 are coupledto the same Fault node (or wire), the wired-OR skill should be used forthis connection. This can be achieved by connecting source-only FToutputs together with a common pull-low device coupling to the Faultnode (or wire). Or, it can also be achieved by connecting sink-only FToutputs together with a common pull-high device coupling to the Faultnode (or wire) with an inversed logic.

FIG. 19 shows another embodiment of the present invention. Thisembodiment is different from the embodiment shown in FIG. 7 in that, thelocal circuit 56 of this embodiment may be coupled to multiple lightemitting device strings 54, for example but not limited to two lightemitting device strings 54 as shown in FIG. 19, wherein the nodes CS1and CS2 of the local circuit 56 are coupled to the second ends E2 of twodifferent light emitting device strings 54 respectively.

FIG. 20 shows another embodiment of the present invention. Thisembodiment is different from the embodiment shown in FIG. 7 in that, thelocal circuit 56 of this embodiment further receives serial data forsetting at least an internal parameter of the local circuits 56. Forexample, a parameter of the current source in each local circuit 56 maybe set individually such that currents through different light emittingdevice strings 54 can be set respectively. The serial data is deliveredby, for example but not limited to, an inter-integrated circuit (I2C)data bus as shown in the figure. As shown in the figure, the localcircuits 56 receive serial data SDA and a clock signal SCK, anddifferent local circuits 56 can respectively adjust their internalparameters, such as current through the light emitting device string 54,or various reference voltages, etc., according to the serial data SDAand the clock signal SCK.

FIG. 21 shows another embodiment of the present invention. Thisembodiment is similar to the embodiment shown in FIG. 20 in that, thelocal circuit 56 of this embodiment receives serial data to adjustcurrent through the light emitting device strings 54 (or other internalparameters). This embodiment is different from the embodiment shown inFIG. 20 in that, the serial data is delivered by, for example but notlimited to, a one-wire data bus, wherein the one-wire data bus mayinclude: an asynchronous data bus, a secure socket layer (SSL) data bus,or a tri-state data bus. As shown in the figure, the local circuit 56receives serial data SDI, and different local circuits 56 canrespectively adjust their internal parameters, such as current throughthe light emitting device string 54, or various reference voltages,etc., according to the serial data SDI.

As shown in FIG. 22A, a serial data bus decoder 568 may be provided inthe local circuit 56 in correspondence to the embodiment shown in FIG.20. The serial data bus decoder 568 decodes the serial data SDA and setsthe internal parameter according to the serial data SDA and the clocksignal SCK. As shown in FIG. 22B, a one-wire serial data bus decoder 569may be provided in the local circuit 56 in correspondence to theembodiment shown in FIG. 21. The one-wire serial data bus decoder 569decodes the serial data SDI and sets the internal parameter according tothe serial data SDI.

In the aforementioned embodiments, if the power management circuit 40 isa DC-DC convertor, it may be, but is not limited to, a synchronous orasynchronous buck, boost, or inverting conversion circuit as shown inFIGS. 23A-23H, wherein if the output voltage Vout is a negative voltage,the light emitting devices need to be reversely connected, and thecircuit needs to be modified correspondingly. For example, meanings ofthe high level and the low level of the output of the comparator 563 andthe Smith trigger 564 may need to be interchanged. The valley detectioncircuit 562 may need to be changed to a peak detection circuit, and theinternal supply voltage Vcc and ground GND may need to be coupled toother sources, etc.

The present invention has been described in considerable detail withreference to certain preferred embodiments thereof. It should beunderstood that the description is for illustrative purpose, not forlimiting the scope of the present invention. Those skilled in this artcan readily conceive variations and modifications within the spirit ofthe present invention. For example, a device which does notsubstantially influence the primary function of a signal can be insertedbetween any two devices in the shown embodiments. For another example,the local circuits 56 in the FPD may each be coupled to a differentnumber of light emitting device strings 54 instead of all coupled to thesame number of light emitting device string(s) 54. For another example,the light emitting device is not limited to a light emitting diode asshown in the aforementioned embodiments, but it may be any DC-controlledlight emitting device. For another example, meanings of the high and lowlevels of the digital signals are interchangeable, with correspondingamendment of the circuits processing these signals. In view of theforegoing, the spirit of the present invention should cover all such andother modifications and variations, which should be interpreted to fallwithin the scope of the following claims and their equivalents.

What is claimed is:
 1. A flat panel display (FPD), comprising: a displaymodule for displaying an image; a power management circuit, whichconverts an input voltage to an output voltage according to a feedbacksignal; a plurality of light emitting modules for illuminating thedisplay module, each light emitting module including: at least one lightemitting device string, each light emitting device string having one ormore light emitting devices connected in series, and each light emittingdevice string having a first end and a second end, wherein the first endis coupled to the output voltage for receiving power; and a localcircuit for controlling current through the light emitting device stringand generating a local feedback signal, wherein the local circuit has afirst terminal for receiving power, a second terminal for coupling tothe second end of the light emitting device string to control thecurrent through the light emitting device string, a third terminal forgenerating the local feedback signal, and a fourth terminal for couplingto ground; wherein the local feedback signal of each light emittingmodule is coupled to a first node for providing the feedback signal atthe first node; and a common wiring cluster including: an output voltagecommon wire for delivering the output voltage; a feedback signal commonwire for delivering the feedback signal; and a ground common wire;wherein each light emitting module is electrically coupled to each ofthe common wires.
 2. The FPD of claim 1, wherein the local circuitfurther includes a fifth terminal for receiving a dimming signal toadjust current through the light emitting device string.
 3. The FPD ofclaim 2, wherein each local circuit of the multiple light emittingmodules receives the same dimming signal to commonly adjust currentthrough each light emitting device string, and the common wiring clusterfurther includes a dimming common wire for delivering the dimmingsignal.
 4. The FPD of claim 2, wherein the local circuit furtherincludes a sixth terminal for outputting a phase-shifted dimming signalgenerated by phase-shifting the dimming signal received from the fifthterminal.
 5. The FPD of claim 1, wherein the local circuit furtherincludes a fifth terminal for outputting a local fault signal toindicate a fault condition, wherein the local fault signal of each lightemitting module is coupled to a second node.
 6. The FPD of claim 1,wherein the local circuit further receives serial data for adjusting aninternal parameter of the local circuit.
 7. The FPD of claim 6, whereinthe serial data is delivered by an inter-integrated circuit (I2C) databus or a one-wire data bus.
 8. The FPD of claim 7, wherein the one-wiredata bus includes: an asynchronous data bus, a secure sockets layer(SSL) data bus, or a tri-state data bus.
 9. The FPD of claim 1, whereinthe local circuit includes: a current source for controlling the currentthrough the light emitting device string via the second terminal; and asink-only voltage follower for generating the local feedback signalaccording to a voltage at the second terminal.
 10. A light emittingmodule for use in a flat panel display (FPD), the light emitting modulecomprising: at least one light emitting device string, each lightemitting device string having one or more light emitting devicesconnected in series, and each light emitting device string having afirst end and a second end, wherein the first end is coupled to theoutput voltage for receiving power; and a local circuit for controllingcurrent through the light emitting device string and generating a localfeedback signal, wherein the local circuit has a first terminal forreceiving power, a second terminal for coupling to the second end of thelight emitting device string to control the current through the lightemitting device string, a third terminal for generating the localfeedback signal, a fourth terminal for coupling to ground, and a fifthterminal for receiving a dimming signal to adjust current through thelight emitting device string.
 11. The light emitting module of claim 10,wherein the local circuit further includes a sixth terminal foroutputting a phase-shifted dimming signal generated by phase-shiftingthe dimming signal received from the fifth terminal.
 12. A lightemitting module for use in a flat panel display (FPD), the lightemitting module comprising: at least one light emitting device string,each light emitting device string having one or more light emittingdevices connected in series, and each light emitting device stringhaving a first end and a second end, wherein the first end is coupled tothe output voltage for receiving power; and a local circuit forcontrolling current through the light emitting device string andgenerating a local feedback signal, wherein the local circuit has afirst terminal for receiving power, a second terminal for coupling tothe second end of the light emitting device string to control thecurrent through the light emitting device string, a third terminal forgenerating the local feedback signal, a fourth terminal for coupling toground, and a fifth terminal for outputting a local fault signal toindicate a fault condition.
 13. A light emitting module for use in aflat panel display (FPD), the light emitting module comprising: at leastone light emitting device string, each light emitting device stringhaving one or more light emitting devices connected in series, and eachlight emitting device string having a first end and a second end,wherein the first end is coupled to the output voltage for receivingpower; and a local circuit for controlling current through the lightemitting device string and generating a local feedback signal, whereinthe local circuit has a first terminal for receiving power, a secondterminal for coupling to the second end of the light emitting devicestring to control the current through the light emitting device string,a third terminal for generating the local feedback signal, and a fourthterminal for coupling to ground, wherein the local circuit furtherreceives serial data for adjusting an internal parameter of the localcircuit.
 14. The light emitting module of claim 13, wherein the serialdata is delivered by an inter-integrated circuit (I2C) data bus or aone-wire data bus.
 15. The light emitting module of claim 14, whereinthe one-wire data bus includes: an asynchronous data bus, a securesockets layer (SSL) data bus, or a tri-state data bus.
 16. A lightemitting module for use in a flat panel display (FPD), the lightemitting module comprising: at least one light emitting device string,each light emitting device string having one or more light emittingdevices connected in series, and each light emitting device stringhaving a first end and a second end, wherein the first end is coupled tothe output voltage for receiving power; and a local circuit forcontrolling current through the light emitting device string andgenerating a local feedback signal, wherein the local circuit has afirst terminal for receiving power, a second terminal for coupling tothe second end of the light emitting device string to control thecurrent through the light emitting device string, a third terminal forgenerating the local feedback signal, a fourth terminal for coupling toground, a current source for controlling the current through the lightemitting device string via the second terminal, and a sink-only voltagefollower for generating the local feedback signal according to a voltageat the second terminal.
 17. An integrated circuit for use in a lightemitting module, for connecting to at least one light emitting devicestring, the integrated circuit comprising: a current source forcontrolling current through the light emitting device string via a node;and a sink-only voltage follower, which generates a local feedbacksignal according to a voltage at the node.
 18. The integrated circuit ofclaim 17, further comprising an open detection circuit, which comparesthe voltage at the node with a first reference voltage to determinewhether the light emitting device string is open-circuited.
 19. Theintegrated circuit of claim 18, further comprising a logic gate having afirst input coupled to a start-up indication signal indicating systemstart-up, and a second input coupled to an output of the open detectioncircuit, the logic gate generating an output for determining whether thelocal feedback signal is outputted from the integrated circuit.
 20. Theintegrated circuit of claim 17, wherein the current source is acontrollable current source, which is controlled by a dimming signal.21. The integrated circuit of claim 17, wherein the current source is acontrollable current source, and wherein the integrated circuit furthercomprises: a phase-shift dimming circuit, which receives a dimmingsignal, and generates a phase-shifted dimming signal, wherein thedimming signal or the phase-shifted dimming signal is used forcontrolling the controllable current source.
 22. The integrated circuitof claim 17, further comprising a short detection circuit, whichcompares the node voltage with a second reference voltage to determinewhether the light emitting device string is short-circuited.
 23. Theintegrated circuit of claim 17, further comprising a serial data busdecoder or a one-wire data bus decoder for receiving and decoding serialdata, the serial data being for adjusting an internal parameter of theintegrated circuit.